1. Field of the Invention
This invention relates in general to protection against damage to magnetic head assemblies caused by electrostatic discharge (ESD) during handling and assembly thereof on a suspension assembly for a magnetic storage device, and more particularly to a method of protecting a magneto-resistive (MR) head attached to a suspension assembly against damage caused by ESD.
2. Description of Related Art
MR sensors are well known and are particularly useful as read elements in thin film heads (“MR heads”) for sensing recorded signals on magnetic disks in magnetic disk drive systems used in the computer industry. A typical MR head includes a thin strip of magnetoresisitive material that is positioned between a pair of thin film gap layers, which are in turn sandwiched between a pair of thin film shield layers. The MR head along with a write transducer, which is used for recording information to the magnetic disk, are manufactured using thin film and photolithography process, as part of a slider. The slider is attached to the tip of a flexible member that is cantilevered from an actuator arm for positioning the head relative to the magnetic disk surface to perform read and write operations. This head and suspension assemblage is often referred to in the industry as a head-gimbal assembly or HGA.
As the storage density of disk drives increase, the size of the MR heads are reduced, making it increasingly vulnerable to damage caused by ESD. A major problem that is encountered during manufacture, handling and use of MR heads is the buildup of electrostatic charge on various objects, such as assembly tools and fixtures which come into electrical contact with the heads. The discharge of electrostatic voltages of only a few volts through the MR heads is sufficient to produce electrical current capable of severely damaging or completely destroying the MR heads. Manufacturing yields can therefore be negatively affected because ESD damage may be introduced at any stage during the assembly of the disk drive, and the damaged MR head can only be practically tested and discovered towards the end of the manufacturing process. For those MR heads which were degraded as a result of damage during processing but which passed initial acceptance tests by the manufacturer, the performance, reliability, and service life of the assembled magnetic disk drive having the damaged heads are put into question.
There have been a number of ESD protection schemes adopted in the past. U.S. Pat. No. 5,710,682 assigned to International Business Machines Corporation disclosed an ESD protection scheme for an integrated suspension assembly of the type that uses twisted leads for the read head, which deploys a shorting bar that automatically shorts the read head prior to final assembly. A shorting bar attached to the actuator arm automatically shunts the lead wires of the read head upon absence of support for the record head. This provides an electrostatic discharge path around the read head, rather than through it.
In an integrated lead suspension (ILS) assembly, integrated conductor leads or traces are formed in a layer on the surface of the flexure, instead of twisted wire as described above in U.S. Pat. No. 5,710,682. ILS assemblies are significantly smaller in dimensions compared to integrated suspension assemblies, with leads/traces that are formed in close tolerance and clearance. The leads terminate on contact pads at the end face of the slider; one pair of leads is in electrical connection with the MR head and the other pair of leads is in electrical connection with a write transducer. The other ends of the leads terminate in a multiconnector that extends from the load bearing support structure (e.g., the load beam) of the ILS assembly. For ESD protection, a removable short-shunting strip is provided at the multiconnector to provide an effective means of temporarily protecting the read and write heads from ESD. In the ILS assembly process, the short-shunting strip is maintained, but it must be removed when the ILS assembly is ready to be tested for its functionality or to be installed in a disk drive.
While these earlier schemes were satisfactory in reducing ESD damage to the MR heads in an ILS assembly, they are not without limitation. If the shunting strip remains on the ILS, it is impossible to conduct functionality tests on either MR read sensor, write transducer, or a combination of the two. The shunting strip shunts the ESD transient, but also shunts the signal from the sensors. As a consequence, the shunting strip becomes an issue in the quality control of disk drives. It should be removed at some point in time in the ILS assembly process.
In the past, during the removal of the short-shunting strip, an ESD event may result from static buildup on a tool used to separate the strip, which for example can be an electrically conductive scissor. If the electrical current is large enough, damage can occur to part or all of the recording head. What is needed is a more reliable method for protecting the MR head of an ILS assembly from an ESD event. ESD protection schemes designed for integrated suspension assemblies with twisted wire can be difficult to implement or are not suitable for ILS assemblies, due to the significant size differences between the two types of assemblies. Further, once the short-shunting strip is removed, there is no shunting of ESD available when the ILS assembly is subsequently being handled. It is therefore desirable to provide a means for shunting that remains available on the ILS.